JPH0553424A - Image forming device - Google Patents

Abstract

PURPOSE:To form an image with a nearly constant density even when toner in a developer is being consumed by providing a toner remaining quantity detecting sensor and a developing bias control means. CONSTITUTION:A sensor 30 for nearly linearly detecting a toner remaining quantity in a developing unit 14 and a developing bias control means 31 for changing-controlling a developing bias according to a sensor output are provided. Accordingly, a developing bias voltage is changing-controlled according to a toner remaining quantity in the developing unit 14 so that, even when toner difficult to be electrified is remaining due to toner consumption, an appropriate developing bias for compensating the shortage of electrification is determined to be imparted to the developing device 14. Since a specified potential difference is formed between an image carrier 12 surface and the developing unit 14 so as to conduct sufficient toner attraction to the image carrier 12, image forming can be carried out with nearly constant density until toner is almost consumed. Consequently, low density (light) printing is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic transfer type image forming apparatus.

[0002]

2. Description of the Related Art A two-component developer used in an electrostatic transfer type image forming apparatus is a toner for visualizing an electrostatic latent image on a photoconductor and a toner by triboelectric charging and developing the toner in a developing area. It is composed of a carrier to be transported to. The carrier is not consumed by execution of copying and is always held in a constant amount in the developing device. On the other hand, the toner is consumed by executing copying. In the so-called 1.5-component developer, the toner is a magnetic toner, and like the above-described two-component developer, the magnetic toner is consumed by executing copying.

[0003]

However, toners (including magnetic toners, the same applies hereinafter) vary in particle size (for magnetic toners, for example, 5 to 10 μm), and the amount of charge varies depending on the particle size. However, there is a property that those that are easily charged are consumed and those that are difficult to be charged remain. For this reason, the toner in the developer is consumed, the remaining amount of the toner is reduced, and if the toner that is difficult to be charged remains, the toner is not sufficiently adsorbed onto the image carrier, and as shown in FIG. In addition, there is a problem that the image density is reduced.

If such an image forming apparatus is used in a copying machine, it is sufficient to operate the image density adjustment key to increase the print density and perform another copy, but the copy is wasteful. Will occur. Further, when such an image forming apparatus is used in a facsimile machine, in the facsimile reception, normally, the process of printing the received contents cannot be performed again unless the memory is received. Therefore, the sender is requested to retransmit the contents. It also causes problems such as having to do so.

In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus capable of forming an image with a substantially constant density even when the toner in the developer is consumed.

[0006]

In order to solve the above-mentioned problems, an image forming apparatus according to the present invention develops a sensor for detecting the remaining amount of toner in a developing device substantially linearly, and a developing device according to the sensor output. And a developing bias control means for changing and controlling the bias.

[0007]

According to the above construction, since the developing bias voltage is changed and controlled according to the remaining amount of toner in the developing device, even if toner that is difficult to be charged due to toner consumption remains, the insufficient charging amount can be compensated. An appropriate developing bias is set and this is applied to the developing device, and a predetermined potential difference is formed between the surface of the image carrier and the developing device so that the toner is sufficiently attracted to the image carrier. Therefore, it is possible to form an image with a substantially constant density until the toner is almost consumed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. FIG. 1 is a configuration diagram schematically showing an internal configuration of an image forming apparatus 1 according to the present invention. The image forming apparatus 1 includes a main charger 1
1, a photoconductor drum 12, an optical writing unit 13, a developing device 14, a transfer charger 15, a charge eliminating lamp 16, a cleaner 17, and a high-voltage power supply device A, B, C, and a magnetic sensor 30 arranged in the developing device 14. , This magnetic sensor 30
And a developing bias control means 31 connected to the high-voltage power supply device B.

The main charger 11, the developing device 14,
A high voltage is applied to each of the transfer chargers 15. First, with respect to the main charger 11, a high voltage of about −5 KV is applied by the high voltage power supply device A. In the drawing, a scorotron charger having a grid electrode 111 is used as the main charger 11, but in this case, the unevenness of the charging potential on the surface of the photoconductor drum 12 is significantly larger than that in the case of using a normal charging charger. Can be reduced to Here, the grid electrode 111 is normally applied with a bias of about −700 V to regulate the charging potential of the surface of the photosensitive drum 12.

In the developing device 14, the high-voltage power supply device B is used for the developing roller (having a developing sleeve on the surface of the magnet roller) 140, and the high-voltage power supply device B is used in the range of -450 to -550V. The developing bias is applied at. Magnetic sensor 30
Is for detecting the remaining amount of toner in the developing device 14. For example, a change in the amount of magnetic toner existing in the developer is detected by a change in magnetic permeability to detect the remaining amount of toner. The change in magnetic permeability is converted into a substantially linear voltage change, which is supplied to the developing bias control means 31 as a sensor output.

The developing bias control means 31 obtains the sensor output of the magnetic sensor 30 and changes and sets the developing bias in the high-voltage power supply device B to any voltage of -450 to -550V. FIG. 3 is a graph showing the relationship between the remaining toner amount (sensor output) and the developing bias setting value in the high voltage power supply device B. As can be seen from this graph, if the toner remaining amount is large (the sensor output voltage value is high), the developing bias value is set high, and if the toner remaining amount is low (the sensor output voltage value is low),
Control is performed to set the developing bias value low. However, regarding the relationship between the remaining toner amount and the sensor output, in this embodiment, the sensor output value is 2 V or more when the remaining toner amount is sufficient, and the sensor output value is 1 V when the toner is almost consumed. It will be below.

The relationship between the developing bias and the print density is as shown in FIG. 4, and the lower the developing bias, the more
The print density is high (dark). In the image forming apparatus 1 as described above, a series of image forming processes including exposure and development are performed as follows. Photoconductor drum 1
As 2 rotates in the direction indicated by arrow X, the main charger 11 uniformly charges the surface of the photosensitive drum 12. Next, the surface of the charged photosensitive drum 12 is irradiated with light corresponding to an image by the optical writing unit 13 including an LED array or the like. At this time, the charged electric charge is removed from the exposed portion corresponding to the image, while the non-exposed portion remains in the electric charge, and an electrostatic latent image is formed on the photosensitive drum 12. Then, the developing device 14 supplies the toner charged to the same polarity as the electrostatic latent image to the surface of the photosensitive drum 12.

Here, the amount of toner remaining in the developing device 14 is detected by the magnetic sensor 30, and the sensor output of the magnetic sensor 30 is input to the developing bias control means 31, which develops the above. The developing bias is set in accordance with the output of the sensor, and the set developing bias is applied to the developing roller 21 by the high-voltage power supply device B.

In the setting control of the developing bias, as shown in the flowchart of FIG. 2, first, the remaining toner amount is detected before the development is started (S1), and then the sensor output value (V _T) is determined whether the below 2V (S2), if not below 2V, set the developing bias voltage (V _B) to -450 V (S3), the process proceeds to step 8. On the other hand, if the sensor output value (V _T) is less than 2V, the sensor output value (V _T) is determined whether 1V or less (S
4) If it is 1 V or less, a notification buzzer (not shown) is sounded (S5), the printing operation is stopped (S6), and the process is ended. Incidentally, if the user by informing buzzer above supply toner of a predetermined amount, or by the like replacing the developing unit 14, the sensor output value (V _T) becomes more 2V,
After step 3, the developing bias voltage (V _B ) is −450.
It is set to V.

On the other hand, if the sensor output value (V _T ) is not less than 1 V, the developing bias voltage (V _B ) = (V _T −1) ×
The arithmetic processing of 100-550 is executed (S7), and the developing bias is output at the voltage thus set (S8).
When the toner is electrostatically attracted to the exposed portion by the above development processing to form a toner image, the recording paper D is conveyed so as to overlap the toner image formed on the photosensitive drum 12, and the recording paper D is conveyed. With respect to D, when a charge having a polarity opposite to the charging polarity of the toner is applied from the back side by the transfer charger 15, a suction force is generated and the toner image on the photosensitive drum 12 is transferred onto the surface of the recording paper D. .. Then, the recording paper D after the transfer is applied with heat and pressure by a subsequent fixing device (not shown), and the toner image is fused on the recording paper D to become a permanent image. On the other hand, regarding the photosensitive drum 12 after transfer,
The cleaner 17 removes the toner remaining on the photoconductor drum 12 without being transferred by the charge removing lamp 16.
Will be removed.

According to the above construction, since the developing bias voltage is controlled to be changed according to the remaining amount of toner in the developing device 14, even if toner which is difficult to be charged due to toner consumption remains, the insufficient charging amount is compensated. An appropriate developing bias for the photosensitive drum 1 is set and applied.
(2) A predetermined potential difference can be formed between the surface and the developing device 14 so that the toner can be sufficiently adsorbed onto the photosensitive drum 12, so that an image is formed at a substantially constant density until the toner is almost consumed. Can be done.

Therefore, when the image forming apparatus is used in a copying machine, waste of paper due to copying again is prevented, and when the image forming apparatus is used in a facsimile apparatus, the image is retransmitted to the transmitting side. Problems such as having to request transmission can be eliminated.
In this embodiment, when the sensor output value (V _T) becomes 1V or less, by sounding a notification buzzer it has been decided to stop the printing requesting toner replenishment, ringing or notification of a notification buzzer lamp lighting (blinking) relatively early stage and (e.g., when 1.1 V) is performed in, while requesting the toner supply to the user, a constant concentration subsequent to the sensor output value (V _T) is less than 1V May be printed.

In this embodiment, the magnetic sensor is used as the sensor for detecting the toner remaining amount in the developing device 14 almost linearly, but an optical sensor or a bulk change detecting sensor may be used.

[0019]

As described above, according to the present invention, since an image can be formed with a substantially constant density even when the toner is consumed, it is possible to prevent low density (light) printing. Therefore, it is possible to solve the problems such as waste of paper due to copying again, and the need to request the sender to send again.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming mechanism portion in an image forming apparatus as an embodiment of the present invention.

FIG. 2 is a flowchart showing control for changing a developing bias voltage.

FIG. 3 is a graph showing the relationship between the remaining toner amount and the developing bias setting value.

FIG. 4 is a graph showing a relationship between a developing bias value and print density.

FIG. 5 is a graph showing the relationship between the remaining toner amount and the print density.

[Explanation of symbols]

 14 developing device 30 magnetic sensor 31 developing bias control means B high-voltage power supply device

Claims (1)

[Claims] 1. An image forming apparatus comprising: a sensor for detecting a remaining amount of toner in a developing device substantially linearly; and a developing bias control means for changing and controlling a developing bias according to an output of the sensor.